Fillers for cigarettes include cut tobacco obtained by cutting raw materials, such as leaf tobacco from which main ribs are removed, the main ribs and the reconstructed tobacco, separately or by mixture. Alternatively, the fillers include cut tobacco subjected to an expanding process. Both kinds of cut tobacco have the given grading, that is, size.
In such a cut tobacco-forming process, cut tobacco is generally subjected to a liquid flaver-adding process, namely a flavoring process, so that the cut tobacco, which has undergone this process, has a high moisture content. Therefore, after the flavoring process, the cut tobacco needs to be dried to contain the desired moisture content before being fed to a cigarette making machine. The cut tobacco subjected to the expansion process contains not only a high moisture content but also an impregnant (liquid carbon dioxide).
Utilized in the cut tobacco-drying process in general are a cylinder dryer or a flash dryer. The flash dryer is capable of drying the cut tobacco in a short period of time, compared to the cylinder dryer, so that it has high drying processibility and is suitable for improving the productivity of cigarettes.
A flash dryer of this type generally comprises a gas flow path through which a dry gas flows, and also includes an air blower, a heater, a cut tobacco-receiving section and a cut tobacco-separating section that are each disposed in the gas flow path in order from the upstream side of the gas flow path.
The cut tobacco fed through the receiving section into the gas flow path is transferred from the receiving section toward the separating section with a dry gas flow and dried in this transferring process. After being dried, the cut tobacco is separated from the dry gas flow in the separating section and taken out of the separating section.
In cases where the cut tobacco is subjected to the drying process, the cut tobacco must be dried evenly. When the drying of the cut tobacco is uneven, for instance, if the cut tobacco is overdried, the cut tobacco generates an irritating odor and loses its flavor and taste. As a result, the quality of the cigarettes is also deteriorated.
Since the cut tobacco is dried in the transferring process as described, there needs to be enough length of the gas flow path from the receiving section to the separating section, namely a drying flow path, for subjecting the cut tobacco to the drying process. This forces the drying flow path to be long. Therefore, the drying flow path has at least one flection, which saves space for installation of the drying flow path.
If there is a flection in the drying flow path, however, the cut tobacco is prone to be fractured when passing the flection. Moreover, the cut tobacco is liable to remain in the flection, and such remaining makes the drying of the cut tobacco uneven.
It is said that smoke, which is generated from the cut tobacco during the burning of cigarettes, contains toxic components. Therefore, if the flash drying of the cut tobacco reduces the toxic components contained in the smoke, the flash dryer is more suitable for drying the cut tobacco.